The present invention relates to a magnetron driving power supply circuit in an electronic range and more particularly to a magnetron driving power supply circuit of the small, light inverter type for the use of the electronic range in commercial power sources with commercial voltages (AC 110 V/220 V) and frequencies (50/60 Hz).
In electronic ranges, there have been conventionally used the magnetron driving power supply circuits of the ferro-resonance transformer type wherein a ferro-resonance transformer may be used and the inverter type wherein a high voltage may be obtained by switching a boosting transformer at high speed.
FIG. 1 is a schematic diagram of the conventional magnetron driving power supply circuit of the ferro-resonance transformer type. As shown in the drawing, the magnetron driving power supply circuit comprises a ferro-resonance transformer T1 having its primary coil connected to a commercial power source (AC) via a switch SW1 and its secondary coil connected to a magnetron MGT via a high voltage condenser C1 and a high voltage diode D1. This circuit constitutes a half-wave voltage doubler rectifier circuit which doubles output voltage from the secondary coil during half cycles and supplies the doubled voltage to the magnetron MGT.
When AC 110 V power is supplied from the commercial power source (AC), the switch SW1 is connected to an AC 110 V selecting terminal (a) of the primary coil of the ferro-resonance transformer T1 to apply the AC 110 V power from the commercial power source (AC) to the primary coil. On the other hand, when AC 220 V power is supplied from the commercial power source (AC), the switch SW1 is connected to an AC 220 V selecting terminal (a) of the primary coil of the ferro-resonance transformer T1 to apply the AC 220 V power from the commercial power source (AC) to the primary coil. Therefore, a constant voltage can be outputted from the secondary coil of the ferro-resonance transformer T1 by the adjustment of the number of windings of the primary coil and the secondary coil of the ferro-resonance transformer T1.
Therefore, when AC 110 V power is supplied from the commercial power source (AC), the switch SW1 is connected to the AC 110 V selecting terminal (a) of the primary coil of the ferro-resonance transformer T1 and therefore applies the AC 110 V power from the commercial power source (AC) to the primary coil. Then the AC 100 V voltage is boosted by the ferro-resonance transformer T1 up to about AC 2000 V to be outputted from the secondary coil. Thereafter, the AC 2000 V voltage from the secondary coil of the ferro-resonance transformer T1 is doubled by the half-wave voltage doubler rectifier circuit comprised of a high voltage condenser C1 and a high voltage diode D1 during half cycle.
As a result, about 4000 V power obtained in this manner is supplied to the magnetron MGT to drive it.
However, the above-mentioned conventional magnetron driving power supply circuit of the ferro-resonance transformer type can not be small and light because of large sizes and volumes of its ferro-resonance transformer and its high voltage condenser. Further, its design has to be modified depending upon the commercial frequency (50 Hz/60 Hz).
FIG. 2 is a schematic diagram of the conventional magnetron driving power supply circuit of the inverter type. As shown in the drawing, the magnetron driving power supply circuit comprises a noise stopping coil L1 for inputting AC power from a commercial power source (AC) and stopping noise of the AC power, a bridge diode BD1 for rectifying output power from the noise stopping coil L1, a condenser C2 for smoothing the rectified power from the bridge diode BD1, and a resonance condenser C3 for inputting the smoothed power from the condenser C2 through an overcurrent stopping choke coil L2. The power supply circuit also comprises a boosting transformer T2 having its primary coil for inputting the smoothed power from the condenser C2 through the overcurrent stopping choke coil L2 and a switching transistor Q1 connected to the resonance condenser C3 and the primary coil of the boosting transformer T2 for switching at high speed to control current flowing through the resonance condenser C3 and the primary coil of the boosting transformer T2. The supply circuit also comprises a protecting diode D2 connected to the resonance condenser C3 and the primary coil of the boosting transformer T2 for protecting the transistor Q1, a current detector 1 for detecting the current flowing through the primary coil of the boosting transformer T2 via and a current transformer CT, a switching controller 2 responsive to the detected current signal from the current detector 1 for outputting a switching control signal. The supply circuit also comprises a switching transistor driver 3 responsive to the switching control signal from the switching controller 2 for controlling the ON/OFF operation of the transistor Q1, and a high voltage condenser C1 and a high voltage diode D1 which constitute a half-wave voltage doubler rectifier circuit which doubles high voltage output from a secondary coil of the boosting transformer T2 during half cycles and supplies the doubled voltage to a magnetron MGT to drive the magnetron MGT.
The switching transistor Q1 is switched at high speed, about 20 KHz-40 KHz in response to the switching control signal that the switching controller 2 outputs in response to the detected current signal from the current detector 1, so that it controls the current flowing through the primary coil of the boosting transformer T2. Therefore, AC 2000 V voltage of high frequency is induced in the secondary coil of the boosting transformer T2. Then the AC 2000 V voltage from the secondary coil is doubled by the half-wave voltage doubler rectifier circuit comprised of high voltage condenser C1 and high voltage diode D1 during half cycles to drive the magnetron MGT. On the other hand, voltage induced in another secondary coil of the boosting transformer T2 is supplied to a filament of the magnetron MGT.
However, because a high voltage of high frequency is induced in the secondary coil of the boosting transformer T2, a reactance is small, resulting in small volume of the boosting transformer T2 and small capacity of the high voltage condenser C1.
Therefore, the magnetron driving power supply circuit of the inverter type has weight reduced by about 1/4 relative to a magnetron driving power supply circuit of the ferro-resonance transformer type. This is because of the small volume of its boosting transformer T2 and the small capacity of its high voltage condenser C1 as stated previously. Therefore, the supply circuit can be smaller and lighter.
The conventional magnetron driving power supply circuit of the inverter type as above-mentioned, however, cannot be applied to commercial power sources of the different types at a time, since capacities of its boosting transformer T2 and its high voltage condenser C1 have to be modified depending upon AC 110 V/220 V powers from commercial power sources.